Process of clarifying a liquid suspension of finely divided solids



United States Patent 3,276,998 PROCESS OF CLARIFYING A LIQUID SUSPENSION OF FINELY DIVIDED SOLIDS Jerome Green, Chicago, Ill., assignor to Nalco Chemical Company, Chicago, [1]., a corporation of Delaware No Drawing. Original application Feb. 17, 1956, Ser. No. 566,077, now Patent No. 3,130,167, dated Apr. 21, 1964. Divided and this application Jan. 23, 1964, Ser. No. 339,618

7 Claims. (Cl. 210-52) This application is a division application of my copending application Serial No. 566,077, filed February 17, 1956, now US. Patent No. 3,130,167.

This invention relates to a method of coagulating and producing settling of finely divided solids, especially those which are predominantly inorganic and normally remain suspended in water, more particularly dilute suspensions in water containing concentrations of predominantly inorganic solids within the range of about 0.001 10 parts per million) to about 25% by weight of said suspensions.

Among the most difiicult industrial problems is the clarification of industrial wastes which would otherwise create a nuisance and cause pollution of lands and streams. Examples of such wastes are phosphate mine waters, coal washing waters, clay suspensions, calcium carbonate suspensions, and other suspensions of finely divided solids in water which result from industrial processes such as mining, washing, purification, and the like. These suspensions normally contain the solid materials in very finely divided form in concentrations within the range of about .001% to about 3% by weight of the suspension and sometimes in amounts up to about 25% by weight of the suspension. Such suspensions will remain stable for days and many of them are not affected by the addition of ordinary coagulants such as alum. If the solids are allowed to remain in suspension the resultant suspension cannot be utilized for industrial processes and also presents a disposal problem.

One of the special problems with which the present invention is concerned is the improvement of fioc size and settling in hot phosphate softening processes. In such processes waters containing hardness components, such as calcium and magnesium, are treated with phosphates to form insoluble calcium and magnesium phosphate salts which settle out and are separated by filtration. Orthophosphates, such as anhydrous 'disodium phosphate, are often employed for this purpose. In this type of process, the precipitated inorganic solids are very finely divided with the result that coagulation and settling are relatively slow and its is diflicult to produce a water free from turbidity. Various coagulation aids have heretofore been employed in an effort to improve floc size and settling but many of the materials which function satisfactorily as coagulants in clarifying other types of turbid waters leave much to be desired, and in many cases are ineffective for practical pmposes, when employed as coagulation aids in hot phosphate softening processes.

Patented Oct. 4, 1966 The expression phosphate softening as used herein refers to a process in which a water-soluble phosphate which forms insoluble calcium and magnesium salts is added to water containing calcium and/or magnesium salts in order to reduce the concentration of calcium and/or magnesium in the water by precipitation as an insoluble phosphate. Hot phosphate softening is frequently used as a primary softening in low hardness waters. It is often used as a secondary softening following lime softening of high hardness waters. The term lime softening includes those processes in which lime is employed either alone or in conjunction with minor amounts of soda ash or alkaline materials such as sodium aluminate for the treatment of water .to separate the hardness components by precipitation. In the hot softening processes temperatures of 180 F. to 275 F. (under pressure) are frequently employed, the preferred temperatures being within the range of 212 F. to 240 F. Some types of chemicals which are useful in coagulation for other purposes tend to undergo chemical changes and are practically ineffective as coagulation aids in hot phosphate softening processes.

One of the objects of the present invention is to provide a new and improved method for coagulating and producing settling of finely divided, predominantly inorganic solids from relatively dilute suspensions in water.

Another object of the invention is to provide a new and improved process for coagulating and producing settling of finely divided solids which are predominantly inorganic and normally remain suspended in water in con centrations of 0.001% to. 25 by weight of the suspen- SlOIl.

A further object of the invention is to provide a process of treating suspensions of the type described in which relatively small amounts of added substances will produce settling of the finely divided solids without introducing into the liquid substances which have a harmful effect on industrial processes or cause harmful pollution of streams.

An additional object of the invention is to provide a process of improving floc size and settling in softening processes, especially in hot phosphate softening. Other objects will appear hereinafter.

In accordance with the invention it has been found that it is possible to produce improved results in the coagulation and settling of finely divided solids which are predominantly inorganic and normally remain suspended in water in concentrations of 0.001% to 25% by weight of the suspension by treating said aqueous suspensions with a small amount, preferably .25 part to 15 parts per million, but sometimes as much as parts per million, based on the weight of the total suspension, of a composition containing both a coagulating clay and a synthetic water dispersible polymer having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization of at least one monoolefinic compound through the aliphatic unsaturated group, said structure being substantially free of crosslinking.

The polymers which have been found to be especially effective for the purpose of the invention are water-dispersible synthetic polymers having a linear hydrocarbon structure and containing in a side chain a hydrophilic group from the group consisting of carboxylic acid, carboxylic acid anhydride and carboxylic acid salt groups.

The coagulating clays which have been found to be most effective when employed in conjunction with the aforesaid polymers may be described as colloidal clays which hydrate and swell in water, especially bentonite and Saponite. The use of bentonite as a coagulating agent in conjunction with sodium aluminate is shown in US. Patent 2,284,827 and the use of saponite as a clarifying agent for turbid waters is shown in US. Patent 2,420,340. In accordance with the present invention, however, the combined use of such clays and a water dispersible polymer of the type previously described produces results which are not obtained by the use of the individual components of the coagulating composition. In some cases these compositions containing both the clay and the waterdispersible polymer act as aids in forming larger, faster settling precipitates. In other cases they improve the effective removal of the last traces of turbidity. They can also be employed effectively in conjunction with other coagulants such as aluminum sulfate, sodium aluminate, ferric sulfate or ferrous sulfate. For example, they can be added just before or just after, or simultaneously with such other coagulants. The order of addition may vary depending upon the particular type of suspension. It may also vary depending upon whether or not the pH of the suspension is adjusted, for example, by the addition of lime. In general, the order of addition of the compositions employed in the practice of the present invention with respect to other. coagulating agents can be determined by routine experiments. Excellent results are obtained in many instances in producing coagulation and settling by employing compositions of the present invention as the sole coagulating agents, that is, without using them in conjunction with any other type of coagulant.

In general, the compositions of the present invention will contain a minor proportion of a water-dispersible polymer of the type described as compared with the quan tity of coagulating clay. In the preferred compositions of the invention the weight ratio of the water-dispersible polymer to the coagulating clay is within the range. of 1:20 to 1:1.

Examples of compositions which are suitable for the practice of the invention are as follows:

Bentonite 2 4 Composition F Polyvinylmethylether-maleic anhydride 1 Sodium bicarbonate 3 Bentonite 2 The dosage of the coagulating composition employed in the practice of the invention will vary somewhat depending upon the particular type of suspension treated. As previously indicated, however, the dosage will usually be Within the range of .25 part to 15 parts of the. coagulating composition per million parts of the aqueous suspension of finely divided solids, calculated on a weight basis. In some cases, it may be desirable to use as much as parts of the coagulating composition per million parts of suspension.

While especially good results have been obtained by employing as one component of the coagulating composition a synthetic water-dispersible polymer of the type described containing a carboxylic acid group, a carboxylic acid anhydride group of a carboxylic acid salt group in a side chain, excellent results are also obtained by employing water-dispersible hydrophilic copolymers containing also in a side chain another hydrophilic group such as, for example, the nonionic groups of carboxylic acid amide, hydroxy, pyrrolidone, hydroxyalkyl and:

synthetic organic polymers may also contain carboxyw alkyl ester, phenyl, lower alkyl phenyl, alkyl, halogen, carboxylic acid amide, pyrrolidone, a hydroxy, a hydroxy alkyl ether and/ or alkoxy groups in a side chain, all being 1 essentially nonionic. The invention thus contemplates the employment of copolymers which contain only anionic groups or both anionic and nonionic groups.

An important class of synthetic organic polymers employed for the purpose of the invention consists of the synthetic polymeric water-soluble polyelectrolytes having an average molecular weight greater than 10,000 which are copolymers of compounds containing the group and at least one other monoolefinic monomer.

Another important class of synthetic polymers ,em-

ployed for the purpose of the invention consists of syn-v thetic water-soluble polyelectrolytes having a weight average molecular weight of at least 10,000 which are polymers of a compound containing the molecular group wherein n is an integer from zero to 1, inclusive.

The following water-dispersible synthetic organic polymers and their characteristic grouping illustrate the types of polymers which have been found to be effective for the practice of the invention:v

No. Name Characteristic Grouping 1- Polyacrylate sodium salt CHCH C O O N8 2 Polymethacrylic acid sodium salt -CH;(|J-

C 0 O Na 3 Maleic anhydride-vinyl acetate CHCH|CH-CH- CHiC=0 0 O 4 Pcglyiginylmethylether-maleic anhy- CHCH (lJH-CH e. a l

O CH: 0 0:0

7 CH; CH;

5. Methaerylic acld-methacrylamidmun CH,CC H;|C

c 0 o 0 ONE,

6- Polyacryllc acid CHr-CH G O O (3 1 7 Isopropenyl acetate-maleic anhydride CH:CCH-,CH

sodium salt. I

=0 0:0 I I CHaC=0 0 8 Itaconlc acid-vinyl acetate --CCH, -C H,-CH-

H(+) OH=C=O v $H: 9 Methylslzyrene-maleic anhydrlde sodi- CCH:-?H CH- um s ' COO() C0O(-) N8 N 10 Styrene-maleic anhydride sodium salt. CH-CH;CH CH- O0O() C0O() Na N i r 11, Methylmethacrylate-malelc anhydride C-CH:CH CH- sodium salt. I I

COOCH: CO0() C00() N 12 Acrylic acid styrene copolymerl CHCH:CHCH- esters, and the substituted of these polycarboxylic acids. Where the hydrophilic maleic acid derivatives are i used as one of the starting components to form the copolymer the hydrophobic comonomers may be, for example,styrene, alphamethylstyrene, vinyl toluene, chlorostyrenes, vinyl,acetate, vinyl chloride, vinyl formate, vinyl alkyl ethers, alkyl acrylates, alkyl methacrylates, ethylene, propylene, and/or isobutylene.

The foregoing synthetic copolymers are preferably obtained by reacting equimolar proportions of. a polycarboxylic acid derivative and at least one other monomer but certain of the hydrophilic derivatives of unsaturated weight thereof, and the type of suspension being treated.

In general, for effective results the polymer should have a relatively high molecular weight in excess of 10,000 and ordinarily within the range of 15,000 to 100,000.

As will be recognized from the foregoing discussion, generally speaking, the process of the invention involves clarifying a liquid suspension of solids, suspended in an aqueous phase, and comprises the steps of adding to said suspension under flooculatin-g conditions a composition containing at least one of the aforesaid anionic, water soluble polyelectrolyte resins having a structure derived by a method comprising polymerization of at least one monoolefinic compound through the aliphatic unsaturated group and also containing a coagulating clay (hydratable bentonite or saponite), the amount of said composition added to said suspension being sutficient to coagulate the suspended solids and separating the coagulated solids from the aqueous liquid. It should be understood that the expressionseparating the coagulated solids from the aqueous liquid is employed to include and cover separation by settling as well as separation by actually removing the coagulated solids from the water as by filtering and separation by removing water from the coagulated solids, as by decanting or allowing the supernatant water to overflow. Hydratable bentonite and saponite, in water, have a negative or anionic surface charge.

In the preferred practice of the invention the quantity of the polyelectrolyte is within the range of .25 part to parts per million parts of suspension and the quantity of coagulating clay is 2 to 10 times the weight of the polyelectrolyte.

The invention will be illustrated but is not limited by the following examples, in which the quantities are stated in parts by weight unless otherwise indicated.

Example I p.p.m. and 6 p.p.m. of Composition D good coagulation was obtained in each case with good color removal.

The results obtained with Composition C showed substantial effectiveness of this composition as a coagulant but not quite as good as Composition D.

In each of the foregoing tests the coal suspension was agitated with an agitator operating for /2 minute at 90 revolutions per minute (r.p.m.), 2 minutes at 60 rpm. and 5 minutes at 20 =r.p.m. for each additive.

Under the same test conditions a composition composed of 1 part of polyvinylmethylether-maleic anhydride and 9 parts by weight of kaolin produced poor results at a dosage of 60 p.p.m. and 100 p.p.m., the supernatant liquid in these cases being very cloudy.

Example II Composition was employed effectively in coagulating a phosphate softening water at a dosage of 30 p.p.m., calculated as polyvinylmethylether-maleic anhydride.

8 Example III This example illustrates the use of the compositions of the invention as aids to coagulation'in accelerating the coagulation process. To demonstrate this, 700 mlpof Chicago tap water was treated with 25 p.p.m., of clay to produce a turbid water which was then coagulated with '50 p.p.m. of alum. After allowing the floc to settle the top 500 ml. was poured off and the remaining water portion containingthe floc was poured into :a 1 liter Erlenmeyer flask. This resulted in an approximately 175 m1. sample of concentrated sludge. To thissample there was then added enough of Composition E to provide 1 p.p.m. of polyvinylmethylether-maleic anhydride.

The floc size was greatly increased with very good settling.

Example IV The test procedure was the same as in Example I ex cept that the suspension treated was an iron ore water obtained from a hydraulic iron mine and having'a pH of 9.3. Good coagulation was obtained using a dosage of 1 p.p.m., 5 p.p.m. and 15 p.p.m. of Composition E calculated as the polyvinylmethylether-maleic. anhydride.

In other words, /6 of Composition E is polyvinylmethyh ether-maleic anhydride; the total dosages of Composi:

tion E were respectively 6 p.p.m., 30 p.p.m. and p.p.m.

Example V A turbid water was synthetically prepared by adding.

settling was produced."

Example VI Chicago tap water containing 2000 p.p.m. of a mesh coal suspended therein was successfully, coagulated by adding 6 p.p.m., 30 p.p.m. and 90 p.p.m. of Compositions E and F. Good coagulation was obtained with both compositions but better clarification of the supernatant liquid was obtained with Composition F.

The results obtained are subject to some variation depending upon the pH of'the suspension treated. In gen-, eral, the optimum effectiveness is obtained at a pH value between 6 and '8, but the compositions can be employed over a wider pH range from about 3.5 to about 11.5. The optimum effectiveness within this range can be determined by routine experiment.

The invention is especially vuseful in coagulating and producing settling of finelydivided solids which are predominantly inorganic and are present in concentrations of 10 p.p.m. to 30,000.p.p.m. by weight of the total suspension (0.001%10 3%) in water. 7

The use of the invention makes it possible to cause'settling of many different types of solids from aqueous suspension thereof, at a higher rate than has heretofore been possible in many instances. valuable in clarifying turbid waters and in removing from suspensions'suspended solids which would otherwise be objectionable and would interfere with the disposal of various types of waste, waters and wash waters from:in-; dustrial processes.

The floc size was then observed and it was noted. that the size of the floc particles had increased. Good The invention is especially l The invention is also very valuable in coagulating and producing settling of finely divided This invention is hereby claimed as follows:

1. A process of clarifying a liquid suspension of finely divided solids which are predominantly inorganic and are suspended in water in concentrations of 0.001% to 25% by weight of the suspension comprising the steps of adding to said suspension, under flocculating conditions, a coagulant selected from the group consisting of aluminum sulfate, sodium aluminate, ferric sulfate and ferrous sulfate, also adding substantially conjunctively with said coagulant both a hydrophilic, anionic polyelectrolyte resin which is a copolymer of a member selected from the group consisting of maleic acid and maleic anhydride, said resin having a plurality of hydrophilic, ionizable side groups limited to ionizable side groups from the group consisting of carboxylic acid, carboxylic anhydride and carboxylic acid salt radicals derived from said member selected from the group consisting of maleic acid and maleic anhydride, and a coagulating clay which is negatively charged when added to water, in an amount sufficient to accelerate coagulation of said suspended solids, and separating the coagulated solids from the aqueous liquid.

2. A process as claimed in claim 1 in which the quantity of polyelectrolyte is within the range of 0.25 to parts by weight per million parts of said suspension and the weight ratio of said coagulating clay to said polyelectrolyte is within the range from 1:1 to 1.

3. A process as claimed in claim 1 in which said polyelectrolyte resin contains methylet-her groups and maleic anhydride groups recurring as side chains at intervals along a linear chain.

4. A process as claimed in claim 1 wherein said anionic polyelectrolyte resin is a maleic anhydride-vinyl acetate copolymer.

5. A process as claimed in claim 1 wherein said anionic polyelectrolyte resin is the sodium salt of a styrene-maleic acid copolymer.

6. A process as claimed in claim 1 wherein said anionic polyelectrolyte resin is the sodium salt of a methyl methacrylate-maleic acid copolymer.

7. A process of clarifying a liquid suspension of finely divided solids which are predominantly inorganic and are suspended in water in concentration of 0.001% to about 3 by weight of the suspension comprising the steps of adding to said suspension, under flocculating conditions, a coagulant selected from the group consisting of aluminum sulfate, sodium aluminate, ferric sulfate and ferrous sulfate, also adding substantially conjunctively with said coagulant both a hydnophilic, anionic polyelectrolyte resin which is a copolymer of a member selected from the group consisting of maleic acid and maleic anhydride, said resin having a plurality of hydrophilic, ionizable side groups limited to ionizable side groups from the group consisting of carboxylic acid, carboxylic anhydride and carboxylic acid salt radicals derived from said member selected from the group consisting of maleic acid and maleic anhydride and a coagulating clay selected from the group consisting of hydratable bentonite and saponite, in an amount suflicient to accelerate coagulation of said suspended solids, and separating the coagulated solids from the aqueous liquid.

References Cited by the Examiner UNITED STATES PATENTS 2,345,827 4/1944 Olin 21043 2,625,529 1/ 1953 Hedrick et al 210-54 X 2,783,200 2/1957 Crum et al 21054 X 2,817,645 12/1957 Weisgerber 2l053 X 2,941,942 6/1960 Dahlstrom et al. 21053 3,066,095 11/1962 Hronas 21053 OTHER REFERENCES Ruehrwein et al., Mechanism of Clay Aggregation by Polyelectrolytes, Soil Science, June 1952, vol. 73, pp. 485- 492.

MORRIS O. WOLK, Primary Examiner.

M. E, ROGERS, Assistant Examiner, 

1. A PROCESS OF CLARIFYING A LIQUID SUSPENSION OF FINELY DIVIDED SOLIDS WHICH ARE PREDOMINANTLY INORGANIC AND ARE SUSPENDED IN WATER IN CONCENTRATIONS OF 0.001% TO 25% BY WEIGHT OF THE SUSPENSION COMPRISING THE STEPS OF ADDING TO SAID SUSPENSION, UNDER FLOCCULATING CONDITIONS, A COAGULANT SELECTED FROM THE GROUP CONSISTING OF ALUMINUM SULFATE, SODIUM ALUMINATE, FERRIC SULFATE AND FERROUS SULFATE, ALSO ADDING SUBSTANTIALLY CONJUNCTIVELY WITH SAID COAGULANE TOBH A HYDROPHILIC, ANIONIC POLYELECTROLYTE RESIN WHICH IS A COPOLYMER OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF MALEIC ACID AND MALEIC ANHYDRIDE, SAID RESIN HAVING A PLURALITY OF HYDROPHIC, IONIZABLE SIDE GROUPS LIMITED TO IONIZABLE SIDE GROUPS FROM THE GROUP CONSISTING OF CARBOXYLIC ACID, CARBOXYLIC ANHYDRIDE AND CARBOXYLIC ACID SALT RADICALS DERIVED FROM SAID MEMBER SELECTED FROM THE GROUP CONSISTING OF MALEIC ACID AND MALEIC ANHYDRIDE, A COAGULATING CLAY WHICH IS NEGATIVELY CHARGED WHEN ADDED TO WATER, IN AN AMOUNT SUFFICIENT TO ACCELERATE COAGULATION OF SAID SUSPENDED SOLIDS, AND SEPARATING THE COAGULATED SOLIDS FROM THE AQUEOUS LIQUID. 